With regard to automotive vehicles, certain driving operations different from those of normal driving occur when the driver dozes. For example, with a dozing driver, certain abnormal operations, such as maintaining a steering frequency at a significantly low level or providing no steering operation for a certain period of time and thereafter abrupt steering, may be performed. Normally, due to inattention of the dozing driver, steering frequency is unnecessarily increased. Therefore, if specific steering operations apt to occur during a condition wherein a driver is dozing at the wheel can be detected, it is possible to detect when the driver is dozing at the wheel. By accurately detecting dozing of the driver, an appropriate warning can be given to awaken the driver from the dozing state.
On the other hand, even under normal driving conditions, it is occasionally necessary to steer similarly to the specific operations occurring during dozing at the wheel, depending on road conditions. Therefore, there is some possibility of producing a warning erroneously due to improper recognition of dozing. For example, when the vehicle passes from a straight road to a relatively narrow curved road, the steering operation frequency will be relatively low while driving on the straight stretch and thereafter steering operations of relatively high frequency and amplitude will be performed while on the curved road. Thus, if recognition is based on the condition that steering frequency less than a predetermined frequency is maintained for more than a predetermined time period and thereafter abrupt steering is performed, the warning will be given in the above driving condition even through the driver is in a normal conscious state. Therefore, for detecting dozing of the driver, it is quite important to select warning conditions which are quite specific to the dozing state.
Therefore, it is an object of the present invention to provide a doze warning system for a vehicle by detecting an abnormally high frequency of steering operation under a dozing condition of the driver in order to give a warning to the driver.
The above-mentioned and other objects are accomplished by a warning system for vehicle according to the present invention, which detects the frequency of steering operation within a unit time and produces a warning when the detected steering operation frequency exceeds a predetermined frequency which is preset to a frequency higher than that performed during normal driving. Furthermore, according to the present invention, if steering operations in the same direction are performed at an excessive frequency or if an interval between steering operations is longer than a given interval, the discrimination that the vehicle driver is steering through a curve will be made to prevent the device from producing the warning.
According to the preferred embodiment of the invention, the doze warning system for the vehicle comprises steering angle detecting means for detecting steering angle and steering direction and for producing a signal representative of detected steering angle and steering direction, a dozing detecting circuit for counting the occurrences of steering within a predetermined period, for clearing the counted value when the signal value indicative of a constant steering direction exceeds a given value or the frequency of the signal is lower than a predetermined value, and for producing a warning signal when the counted value exceeds a predetermined threshold value, and warning means for producing the warning in response to the warning signal.